An electron multiplier (continuous dynode electron multiplier) is a vacuum-tube that multiplies incident charges. They consist of a series of biased dynodes .( PbO coated surface) that eject secondary electrons when they are struck by an ion, in a process called secondary emission induce emission of roughly 1 to 3 electrons. If an electric potential is applied between this metal plate and another, the emitted electrons will accelerate to the next metal plate and induce secondary emission of still more electrons. This can be repeated a number of times, resulting in a large shower of electrons all collected by a metal anode, all having been triggered by just one.
The avalanche can be triggered by any charged particle hitting the starting electrode with sufficient energy to cause secondary emission. Hence the electron multiplier is often used as an ion detector. It could also be triggered by a photon causing vacuum photoemission of at least one electron. In a photomultiplier tube, a photo-emissive surface is followed by an electron multiplier with several sequential multiplying electrodes called dynodes. Because these electrodes are separate from each other, this might be called a "discrete-dynode" multiplier.
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